This invention relates to stair mounted elevators or lifts, commonly known as stairlifts. In particular, the invention relates to a governor or speed-limiting device to control or brake movement of a stairlift carriage in the event that some failure or malfunction in the drive mechanism, driving the carriage along a stairlift rail, allows the carriage to exceed a predetermined maximum speed.
Stairlifts, in the form of a carriage mounted for movement along a rail, are well known for moving aged or handicapped persons up and down staircases. Typically stairlifts incorporate a drive motor in the carriage, the output of which engages a rack, extending along the rail, via a gearbox. However, if there is a failure of or in the motor, gearbox or rack, the carriage may be left to travel down the sloping rail in an uncontrolled manner.
There is a requirement, at least in the United Kingdom, that stairlifts incorporate an overspeed governor to automatically apply a braking force in the event that component failure or malfunction allows the carriage to exceed a predetermined speed whilst moving down the rail. In the past these devices have tended to be quite complex in form and have only been able to apply a braking force when the carriage is moving in one direction. Thus, depending on which side of the stairway the stairlift apparatus is mounted, a different governor must be used.
It is an object of this invention to provide a governor for a stairlift which addresses the aforementioned problems or which at least provides a useful choice.
Broadly, the present invention concerns a governor apparatus for governing the velocity of a stairlift carriage along a stairlift rail with the stairlift carriage being movable in opposite directions along the longitudinal axis of the stairlift rail. The governor apparatus includes a braking member displaceable into contact with the stairlift rail and operating means being operable, when the speed of the stairlift carriage along the stairlift rail exceeds a predetermined maximum speed, for causing the braking member to engage the stairlift rail. The operating means comprises a guiding surface, rotatable with the movement of the carriage along the stairlift rail, and a follower, which is operatively connected to the braking member, in a sliding contact with the guiding surface for when the speed of the stairlift carriage is less than the predetermined maximum speed.
Said operating means is preferably constructed and arranged to trigger under the influence of a force induced centrifugally. To this end, said operating means preferably includes guide means rotatable with the movement of said carriage along said rail, and a roller in sliding contact with said guide means, said roller being connected to said braking member.
Said roller is preferably mounted for rotation on a first end of an operating lever, the other end of said operating lever being pivotally mounted to said braking member.
Preferably said braking member is mounted for rotation about the same axis of rotation as said guide means, said braking member having cam surfaces which are non-concentric with respect to said axis of rotation.
Preferably said guide means includes an inner guide surface and an outer guide surface, said roller contacting said inner guide surface when the speed of said carriage is below said predetermined maximum, and contacting said outer guide surface when said speed exceeds said predetermined maximum, said outer guide surface being constructed and arranged to allow the position of said roller to be locked with respect to said guide means.
Preferably said outer guide surface includes at least one locking notch sized to receive said roller.
Preferably said braking member has a central, inoperative position in which said braking member is symmetrical about an axis passing through the axis of rotation thereof.
Preferably said governor further includes a catch to retain said braking member, against rotation, in said central position when not under the influence of said operating means.
In a second aspect the invention provides a stairlift carriage including the governor as set forth above.
Many variations in the way the present invention may be performed will present themselves to those skilled in the art. The description which follows is intended as an illustration only and the absence of description of particular alternatives or variants should in no way be applied to limit the scope of the invention. Such description of specific elements which follows should also be interpreted as including equivalents whether existing now or in the future. The scope of the invention should be defined solely by the appended claims.